Upon the operation of an electronic device, there is a possibility that an unintended electromagnetic field is generated and this electromagnetic field interferes with other electronic device as electromagnetic noises. Such a phenomenon is referred to as an Electromagnetic Interference (EMI). In order to prevent the generation of the accident due to this electromagnetic interference, rules with regard to the electromagnetic noise is provided by various countries and regions. A typical one is a self-regulation formulated by the Voluntary Control Council for Interference by Information Technology Equipment (VCCI).
In order to prevent the electromagnetic interference, it is important to identify the place where the electromagnetic noise is generated in the design stage of an electronic device and find out the generation mechanism of the electromagnetic noise. Therefore, it is effective to measure the electromagnetic field leaked from a component such as an IC and a Printed Wiring Board (PWB) with a high spatial resolution. As an apparatus that is used in such a case, “an electromagnetic field distribution measurement apparatus” is known (for example, refer to Japanese Laid-Open Patent Application JP-A-Heisei, 4-230874). The electromagnetic field distribution measurement apparatus serves to perform scan by an electromagnetic field probe in the vicinity of a PWB and an LSI to measure the electromagnetic field distribution in the vicinity thereof. On the contrary, a device to irradiate an electromagnetic field from an electromagnetic field probe so as to identify the place that is fragile at the electromagnetic interference has been also known (for example, refer to Japanese Laid-Open Patent Application JP-P2006-3135A).
FIG. 1 illustrates a common electromagnetic field distribution measurement apparatus. A product under test 100 is placed on a stage 1. An electromagnetic field probe 2 is connected to a scanning device 3. The scanning device 3 is provided with an X-axis driving unit, a Y-axis driving unit, and a Z-axis driving unit, and thereby, the scanning device 3 is capable of performing scanning by the electromagnetic field probe 2 in X, Y, and Z directions. Thereby, the electromagnetic field probe 2 is capable of measuring an electromagnetic field that is irradiated from the product under test 100. By analyzing the output of the electromagnetic field probe 2 with a spectrum analyzer, an electromagnetic field map is created. By extracting a place corresponding to the intensity of signal from that electromagnetic field map, it is possible to obtain information about a place where an electromagnetic noise is generated and a passage of an electromagnetic noise. Further, an electromagnetic field distribution measurement apparatus having a function to rotate the electromagnetic field probe 2 added thereto can also be considered.
With regard to the method of measuring electromagnetic noises, by the International Electrotechnical Commission (IEC), IEC61967-3 is provided as a Technical Specification (TS). According to IEC61967-3, it is required to manage the position of measurement in units of tens of μm in order to make precise measurement on an LSI chip. It is important for measurement of the electromagnetic noise with such a high spatial resolution to precisely control the position of the electromagnetic field probe 2 and remove “displacement of position”.
In order to enhance the spatial resolution further, in recent years, the electromagnetic field probe 2 itself has been miniaturized. For example, as described in Japanese Patent No. 3102420, by using the fine semiconductor process, a minute electromagnetic field probe having the spatial resolution about 10 μm had been developed. In this case, it is necessary to adjust the position of the front end of the electromagnetic field probe 2 to the position of a target of measurement with the accuracy finer than 10 μm. In order to prevent the displacement of the position due to a microscopical vibration, there are cases that the whole electromagnetic field distribution measurement apparatus is mounted on a vibration isolation table 4 as shown in FIG. 1.
The electromagnetic field probe 2 is placed on the electromagnetic field distribution measurement apparatus by using an accurate installation jig. However, as the electromagnetic field probe 2 is miniaturized as described above, it has been becoming difficult to place the electromagnetic field probe 2 on a desired installation position. The manufacture tolerance of the electromagnetic field probe 2 itself has been becoming relatively large compared to the accuracy with regard to a required space coordinate, so that it has been becoming difficult to control the installation position of the electromagnetic field probe 2 in the order of micrometer. As a result, it is becoming difficult to precisely adjust the position of the electromagnetic field probe 2 to the coordinate of a target of measurement only by the machine coordinate of the electromagnetic field distribution measurement apparatus.
In order to precisely adjust the position of the electromagnetic field probe 2 to the coordinate of the target of measurement, a camera 5 is placed on the electromagnetic field distribution measurement apparatus shown in FIG. 1. Obtaining an image of the product under test 100 and the electromagnetic field probe 2 by using this camera, an operator is capable of confirming if the electromagnetic field probe 2 is located on a desired position on the product under test 100 or not.
FIG. 2A is a schematic view for explaining the measuring operation of an electromagnetic field that is irradiated from a product under test 100. As an example thereof, the product under test 100 having a printed wiring board 110 and a wiring 120 that is formed on the printed wiring board 110 is considered. The printed wiring board 110 is manufactured by a material such as glass epoxy. The wiring 120 is formed along the Y direction. The electromagnetic field probe 2 is arranged on the wiring 120 of the product under test 100. This electromagnetic field probe 2 has a probe head 6 at its front end.
FIG. 2B schematically illustrates the cross sections of the probe head 6 of the electromagnetic field probe 2 and the printed wiring board 110. The electromagnetic field probe 2 is a magnetic field probe that is defined by IEC61967-6, for example, and the probe head 6 thereof is manufactured by a multilayer substrate. At this time, in many cases, a magnetic field detection part 6A, which converts a magnetic field into a voltage, a current, and a distortion or the like, is formed on the inner layer of the multilayer substrate of the probe head 6. In this case, the magnetic field detection part 6A cannot be visually observed from the outside.
Generally, in the case of making a measurement of an electromagnetic field with the wiring 120 as a target of measurement, the intensity of the electromagnetic field just above the wiring 120 is high, and the distribution of the electromagnetic field is formed being symmetrical to the center of the wiring 120. Therefore, it is convenient to make a calibration in order to adjust the center of the wiring 120 to the center of the magnetic field detection part 6A. However, the reference point for the calibration does not necessarily be the center of the wiring 120, and this reference point is decided depending on the object of measuring. For simplicity, the operation to adjust the center of the wiring 120 to the center of the magnetic field detection part 6A will be described here. As described above, in a case where the magnetic field detection part 6A is integrated in the multilayer substrate of the probe head 6, the operator is not capable of visually observing the magnetic field detection part 6A from the outside. In such a case, the following operation may be considered in order to adjust the center of the wiring 120 to the center of the magnetic field detection part 6A.
At first, as shown in FIG. 2C, alignment is carried out so that the external edge of the probe head 6 is aligned with the edge of the wiring 120. In this case, the alignment is visually carried out by using a camera 5. In other words, the operator confirms that a machine coordinate X1 of the edge of the probe head 6 is coincident with a machine coordinate X2 of the edge of the wiring 120 on the basis of the image obtained by the camera 5.
On the other hand, it is assumed that the distance from the edge of the probe head 6 to the center of the magnetic field detection part 6A is ΔX1, and the distance from the edge of the wiring 120 to the center of the wiring 120 is ΔX2. Typically, the magnetic field detection part 6A is designed to be formed on the center line of the probe head 6, and the distance ΔX1 can be calculated by the measurement of the outline of the probe head 6. In addition, it is possible to recognize the distance ΔX2 depending on the actual measured value of the width of the wiring 120.
When the alignment shown in FIG. 2C is carried out, the offset value ΔXd of the center line of the magnetic field detection part 6A with respect to the centerline of the wiring 120 is ΔX1-ΔX2. As a result, by correcting the position of the probe head 6 by the offset value ΔXd after the above-described alignment, it is possible to adjust the center line of the magnetic field detection part 6A to the center line of the wiring 120 in principle.
As described above, by using the camera 5, alignment of the magnetic field detection part 6A of the electromagnetic field probe 2 and the wiring 120 is possible in principle. Further, as shown in FIG. 2B, the camera 5 takes images of the probe head 6 and the wiring 120 from an oblique angle. This is because the distance ΔZm between the probe head 6 and the product under test 100 (refer to FIG. 2C) is not more than 1 mm, and the camera 5 cannot be inserted into the gap between the probe head 6 and the product under test 100. In the case of making measurement on a semiconductor chip, the distance ΔZm may be made less than 1 μm because it is necessary to enhance the spatial resolution to the utmost limit.
The inventor of the present application focused on the following points. According to the above-described method using the camera 5, there is a possibility that the alignment of the magnetic field detection part 6A and the wiring 120 of a measurement target may have some errors.
One factor of the errors is a processing accuracy of the fine probe head 6. In the case where the probe head 6 is manufactured by a printed wiring board or a ceramic substrate, it is difficult to trim the edge of this substrate with high accuracy. Depending on the material, a roughness of the surface of the substrate may be in the range of tens μm to hundreds μm. Accordingly, there is a possibility that errors may be generated when carrying out alignment while visually observing the edge of the probe head 6.
In addition, if the magnetic field detection part 6A is formed on the center axis of the probe head 6, the above-described calculation of the distance ΔX1 can be made relatively easily. However, because of reasons of design and manufacture, as shown in FIG. 2C, the magnetic field detection part 6A may be displaced from the center axis of the probe head 6. In other words, there is a possibility that the position where the magnetic field detection part 6A is manufactured is displaced from the design position of the magnetic field detection part 6A. In this case, it is necessary to calculate the distance ΔX1 according to special methods, for example, by using an X-ray or the like, and this also becomes a factor of errors.
Further, as described above, the camera 5 takes pictures of the probe head 6 and the wiring 120 at an oblique angle. As a result, depending on the sharpness of the image, the size of the distance (ΔZm) between the probe head 6 and the wiring 120 or the like, the errors in alignment are increased. Particularly, in a case where the distance cannot be made sufficiently-small, it becomes difficult to visually observe that the coordinate X1 of the edge of the probe head 6 is coincident with the coordinate X2 of the edge of the wiring 120.